This invention relates to a catalytic assembly for abating the smoke generated from the burning of organic materials including fats, proteins, and/or carbohydrates, during food preparation. This invention has particular application for use with broilers and fryers such as are commonly used in fast food restaurants.
In typical broilers and fryers, as used in fast food restaurants, emissions from broiling fatty hamburger, for example, contain carbon monoxide, organic vapors and aerosols which constitute an environmental, health and fire hazard. In present practice, these threats are masked by diluting the smoke with large amounts of air blown into and through kitchens and exhausted through hoods and chimneys to the outside environment. This practice entails costly air conditioning, i.e. heating or cooling. This standard approach does not prevent condensation and buildup of aerosols in hoods and chimneys, and instead merely shifts the same amount of air pollutants (including objectionable odors) from the indoors to the outdoors.
Due to stricter governmental regulations, as well as economic considerations, it is rapidly becoming important to substantially eliminate the smoke generated by cooking apparatus, preferably by oxidizing the contaminants to carbon dioxide and water. Other much less desirable methods include filtration and electrostatic precipitation of only non-gaseous smoke contaminants (leaving carbon monoxide in the exhaust), or thermal incineration at or above 800.degree. C. While incineration oxidizes all organics, this technique entails costly high temperature resistant equipment and additional high fuel expense. Moreover, incinerators can produce noxious NO.sub.x which in turn can only be partially mitigated by yet another investment in heat exchangers and NO.sub.x reduction catalysts.
Oxidation catalyst for cooking emissions are well known in the art. By way of example, U.S. Pat. No. 3,962,561 describes a closed "pyrolytic" self-cleaning oven which is provided with catalytic enamel walls and a "small" oxidation catalyst. The term "small" as used herein in this connection, means a catalyst having a smoke access area several times smaller than the cooking area. Similar units are also described in U.S. Pat. Nos. 3,428,435 and 3,536,457.
Burkhart (U.S. Pat. No. 4,516,486) describes a similar cooking apparatus with a chimney mounted on an enclosure of the cooking area. The chimney supports a small catalyst such as a honeycomb ceramic catalyst, as well as a small electrical (Nichrome) heater. When the catalyst is heated to 600.degree. F. the cooking vapors are burned to yield water vapor and carbon dioxide.
Ookubo et al. (U.S. Pat. No. 4,113,439) also describe a closed cooking apparatus with a small diameter exhaust pipe containing a layered assembly of small catalysts utilizing platinum or MnO.sub.2 -based oxidation catalysts, and at least one oil fume decomposing layer. The oil fume decomposing layer is designed to equalize the amount of oil fumes, and also to play the role of dispersant to make the contact of the oil fumes with the catalyzer as uniform as possible.
A common feature in the art has been the funneling of the smoke from a large fully enclosed cooking area to a small catalyst. The need has arisen for a smoke abatement assembly that is better able to accommodate the sporadic non-uniform smoke release, including practically uncontrollable bursts due to irregular grease flaming that is typical in fast food broiling and frying operations. As recognized by Ookubo et al., many catalysts require a uniform flow of volatile (preferably aerosol-free) contaminants, for substantially complete oxidation thereof. Typically this has required an expensive system involving an enclosed complex cooking apparatus provided witch fans and/or heat distributors, or even extra heaters as above described. Moreover, regardless of cost, such prior systems have not been configured or convenient to retrofit open-top broilers or fryers such as are commonly used under hoods in restaurants. Prior devices have had a tendency to induce changes in heat distribution in the cooking area which adversely affects the quality of the food and the productivity of the cooking process.
Moreover, prior catalyst units have been inadequate for use in conjunction with conveyor broilers typically found in fast-food restaurants. In conveyor broilers successive servings of meat are charbroiled or fried in a continual production line. Conveyor apparatus of this type present a rather demanding environmental emission regulation requirement underlying the required purging and exhausting of the cooking effluent while also preventing the rapid poisoning of the catalytic converters by components of the cooking smoke. There is therefor a need for a catalyst unit that can also be readily adapted for use with conveyor broilers of the fast-food industry.